[surferjoe2007]

Both progesterone and estrogen are necessary for normal breast growth.  Both can also cause temporary swelling from increased blood flow and so on.  Only one or the other may work depending on your existing hormone levels, but taken too far it can cause an imbalance or worsen an existing balance.  And while they’re two of the most major factors they aren’t everything involved and even using both of them may not always work.

More details here, but even this isn’t quite everything: https://en.m.wikipedia.org/wiki/Breast_development

Bio identical estrogen is a great way to fuel breast cancer, especially if you overdose.  I don’t think it causes it directly but it is gasoline waiting for a spark, and the body is constantly killing cancer cells that you never even notice.  There are many studies on estrogen-like herbs for precisely this fear, but usually they find that the herbs decrease cancer risk instead.  Perhaps there are anti cancer compounds next to the estrogen-like components.  IIRC there’s at least 1 study that isolates a single molecule from PM and finds increased cancer risk instead of decreasing cancer risk like many other studies.

Of course there are other ways besides the body’s normal way, like massage and pumping.